The present invention relates generally to a piezo-electric vibrator and, more precisely, a piezo-electric vibrator whose fundamental vibration mode is the thickness-shear mode, like an AT-cut quartz vibrator, a BT-cut quartz vibrator or a ceramic vibrator.
It has experimentally been confirmed by the inventors of this invention that in piezo-electric vibrators of the thickness-shear vibrational mode, there is an "abnormal frequency phenomenon" which is different from the well-known "jump phenomenon", the latter phenomenon being one in which the fundamental main vibration is drawn into a spurious vibration whose mode is different from that of the fundamental main vibration. The "abnormal frequency phenomenon", on the other hand is a phenomenon which is induced by harmonic vibrations whose mode is the same one as the fundamental main vibration. If this "abnormal frequency phenomenon" is present within the working temperatures and load capacitances of the piezo-electric vibrator, this gives rise to various problems such as unsatisfactory performance and unstable operation of the piezo-electric vibrator.